Two very similar genes encode for the Fc-gdelta -receptor III (Fcgdelta RIII, CD16). FcgdeltaIIIA is expressed on NK cells and macrophages and FcgdeltaRIIIB on neutrophils. FcgdeltaRIIIB has two clinically important polymorphisms, NA1 and NA2. In autoimmune neutropenia of childhood neutrophil antibodies are most commonly directed to NA1 or NA2. Neutrophils from people that are NA1 homozygous are more effective at the phagocytosis of opsonized red cells than neutrophils from NA2 homozygous people. Assays using sequence specific primers and the polymerase chain reaction (PCR) have been used to differentiate the two alleles. We developed a new method to genotype NA1 and NA2 with PCR and restriction enzymes. Portions of both FcgdeltaRIIIA and FcgdeltaRIIIB were amplified by PCR, but only the FcgdeltaRIIIB NA 1 PCR product was digested by restriction enzyme XmnI and the FcgdeltaRIIIB NA2 PCR product by Cac81. To validate the assay the NA phenotypes of neutrophils from 45 white people were determined by granulocyte agglutination and were compared with their NA genotype determined by PCR and restriction enzymes. The NA phenotypes and genotypes were the same in all 45 people. The method will used to compare the NA l and NA2 genotypes of Japanese, African American and white people. If unusual genotypes are identified, than donor's neutrophils will be phenotyped and the molecular basis of the polymorphism will be determined. Initial studies show that the NA1 and NA2 gene frequencies in Japanese are 0.70 and 0.30 compared to 0.30 and 0.70 in African Americans and whites.